Smashy smashy is vandalism, property destruction, at a demonstration, protest
march or the like. A common example is breaking
windows.
Smashy smashy is
seen both with and without a hyphen, "smashy smashy" or "smashy-smashy"
There's an article about smashy smashy,
property destruction at protests, called "Why All the Smashy-Smashy? A Beginner's Guide to Targeted
Property Destruction".